A NUTRITIONAL STUDY OF INSECTS 57 



be held in check by the larvae, since if allowed to sporulate, as 

 occurs after death, injury would result. Portier believes the se- 

 cretion of the labial glands have this function. To hnk these 

 observations with the case of Nepticula, in which the larvae are 

 aseptic throughout life, Portier ('11 c) describes the condition in 

 Gracillus syringella, which at first feeds in an aseptic condition 

 on the soft interior of the leaf, and then, after feeding on the ex- 

 terior of the leaf and becoming associated with a digestive flora-' 

 capable of dissolving woody tissues, bores into the twigs, the 

 organisms being in part absorbed by phagocytosis as food for 

 the larvae. 



Internal sjaiibionts have also been found in a beetle, Anobium 

 paniceum, by Karawaiew ('99) and Escherich ('00). These 

 symbionts always occur in definite cells in the anterior end of 

 the midgut. Karawaiew thought he recognized a vacuole in 

 them and therefore considered them to be Flagellates. Escher- 

 ich, however, studied them in hanging drops of sugar solution 

 and determined that they were Saccharomycetes. As these 

 yeasts always occur in the same cells and pass through the pupa 

 into the adult, it is quite likely that they are transmitted through 

 the egg from one generation to another. Escherich found that 

 the number of yeast cells varied with the amount of nourishment 

 taken in the different stages of the insects' metamorphosis, thus 

 they were very numerous in the larva, rare in the pupa, and few 

 in the adult. He therefore concluded that the fungi are inti- 

 mately concerned with the nutrition of the insect. As the Ano- 

 biid feeds mainly on very dry house timbers, the symbiosis with 

 a fungus could very well be of value to the insect in the extraction 

 of food from the wood. 



In general we may conclude that insects overcome the disad- 

 vantages of the chemical and mechanical composition of wood by 

 association with microorganisms either as food or as internal 

 symbionts. 



23 Henseval, M. (compare Biedermann) ascribes an antiseptic property to an 

 essential oil secreted by Cossus ligniperda larvae. This oil has the property of 

 making the wood more workable ('angreifbar'). 



